Pedogenesis of coal gangue heaps in high-altitude plateau areas driven by the in-situ formation of layered double hydroxides

Abstract

Although soil pedogenesis has advanced for low-altitude coal gangue piles, current technologies remain unstable and costly in high-altitude, cold mining areas. This study presents an innovative technique employing CaSO₄·2 H₂O and MgSO₄·7 H₂O as mineralizers to accelerate the chemical weathering of coal gangue through the in-situ formation of layered double hydroxides (LDHs), thereby stimulating in-situ pedogenesis to restore the mining areas. The introduced mineralizers interacted with dissolved Al^3 + and Fe³⁺ ions in the coal gangue, forming nano- and micro-scale LDHs with super-stable mineralized structures (K_sp<10⁻⁵⁰), disrupting the original equilibrium of coal gangue, as confirmed by structural characterization and density functional theory (DFT) calculations. Three years of large-scale improvement demonstrated successful pedogenesis with a 10 cm-thick upper soil layer, and the emergence rate of Festuca sinensis, Poa crymophila, Poa pratensis, and Elymus nutans increased from nearly 0.0–93.7 %, showing unprecedented stability under harsh environmental conditions, and significantly reducing costs (approximately $900/year). The leaching concentrations of trace elements were below the limits specified by both the Chinese national standard GB 5749–2022 and the U.S. Environmental Protection Agency (EPA) guidelines, confirming the environmental safety of the technology. This innovative approach offers a significant breakthrough in the remediation of coal gangue heaps in high-altitude mining areas.